ABERYSTWYTH, WALES—BBC News reports that an ongoing heat wave in Britain has resulted in the emergence of crop marks across Wales. Crop marks form when dry conditions parch the landscape, but some vegetation remains green because it draws on the nutrients and moisture trapped in backfilled fortification ditches. The Royal Commission on the Ancient and Historical Monuments of Wales is working to photograph as many of the marks from the air as possible before the next rain. For more, go to “Letter From Wales: Hillforts of the Iron Age.”